Perry I would argue that it is unethical unless the buyers agent is very diligent in telling that same buyer that there may be houses ON THE MARKET that are exactly what this person is looking for and that agent will not show that buyer the home.
Additionally if that agent locks the buyer into a representation contract, then if that buyer does want one of these lower commission homes and is represented by another agent there could be a major problem.
So yes I feel that it is unethical because I do not believe the buyers agent would ever tell a buyer all of this information up front. If they did and they were very up front about it then I guess it is okay but you would have to be a pretty lame buyer to continue to work with someone like that…